As known in the art, saponins are compounds constructed of a triterpene or steroid moiety (aglycon or sapogenin) and one or two glycoside moieties (monodesmosides or bidesmosides, respectively). The aglycon carbon skeleton may be saturated or unsaturated and/or comprise a heteroatom such as nitrogen. The glycoside moiety contains sugars such as galactose, glucose, glucuronic acid, methylpentose, rhamnose and xylose.
The saponin family is known to have a wide range of biological activities such as antimicrobial, antiherbivore and/or cytotoxic activity and their role in nature is likely to be in defense against pathogens, pests and predators. In plants, saponins appear to act as pre-formed antimicrobial barriers to pathogen attack but can also function as suppressors of induced defense responses following hydrolysis [1].
Public concern about the safety of synthetic preservatives used in cosmetic and foods, especially regarding their accumulation and subsequent health effect, have driven health authorities to reduce the applied concentrations or even ban synthetic preservatives. Alternatives such as plant antimicrobial substances are in the focus of many researches, however due to low potency, narrow range and high prices, they are rarely used to replace synthetic preservatives.
The state of the art includes attempts to utilize naturally occurring compounds in cosmetic compositions. For example:
US 2011/0020302 [2] discloses a cosmetic composition comprising natural occurring ingredients having 0.1 to 20 w/w species of Lonicera. 
WO 2000/072861 [3] discloses to a method of extraction bioactive substances such as saponins from plants by supercritical fluid extractions.
WO 1998/048768 [4] discloses a cosmetic composition comprising extracts of species of Camellia and Lonicera as possible additives.
US 2006/0018867 [5] discloses a cosmetic composition comprising polyorganosyloxane-containing epsilon polylysine compounds and an antimicrobial agent. Lonicera japonica extract is mentioned out of a very long list as an anti-inflammatory agent, an astringent, and as a tyrosinase inhibitor. Saponins are mentioned as antimicrobial agents and as pigmentation inhibitor. The publication also teaches optionally adding a saponin as a natural surfactant and/or a humectant.
WO 2009153800 [6] teaches extractions of saponins from Sapindus trifoliatus. 